LTC3731H_15 Datasheet, PDF (25/34 Pages) Linear Technology – 3-Phase, 600kHz, Synchronous Buck Switching Regulator Controller

LTC3731H
Applications Information
of the input capacitor and not share a common ground
path with any switched current paths. The left half of the
circuit gives rise to the “noise” generated by a switching
regulator. The ground terminations of the synchronous
MOSFETs and Schottky diodes should return to the bot-
tom plate(s) of the input capacitor(s) with a short isolated
PC trace since very high switched currents are present.
A separate isolated path from the bottom plate(s) of the
input and output capacitor(s) should be used to tie in the IC
power ground pin (PGND). This technique keeps inherent
signals generated by high current pulses taking alternate
current paths that have finite impedances during the total
period of the switching regulator. External OPTI-LOOP
compensation allows overcompensation for PC layouts
which are not optimized but this is not the recommended
design procedure.
Simplified Visual Explanation of How a 3-Phase
Controller Reduces Both Input and Output RMS
Ripple Current
The effect of multiphase power supply design significantly
reduces the amount of ripple current in both the input and
output capacitors. The RMS input ripple current is divided
by, and the effective ripple frequency is multiplied up by
the number of phases used (assuming that the input volt-
age is greater than the number of phases used times the
output voltage). The output ripple amplitude is also reduced
by, and the effective ripple frequency is increased by the
number of phases used. Figure 13 graphically illustrates
the principle.
SINGLE PHASE
V_SW
I_CIN
I_COUT
V_SW1
V_SW2
V_SW3
I_L1
I_L2
I_L3
TRIPLE PHASE
I_CIN
I_COUT
3731H F13
Figure 13. Single and Polyphase Current Waveforms
3731Hfb
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